(1) Field of the Invention
The present invention relates to a method for preparing a high-purity aqueous quaternary ammonium hydroxide solution.
More specifically, it relates to a method for preparing a high-purity aqueous quaternary ammonium hydroxide solution which comprises reacting a quaternary ammonium organic acid salt with hydrogen peroxide, oxygen or an oxygen-containing gas to produce a quaternary ammonium inorganic acid salt, and then electrolyzing the inorganic acid salt.
(2) Description of the Related Arts
A high-purity aqueous quaternary ammonium hydroxide solution has been used in a wide application range, and for example, it has been utilized as a developing agent for resists in a manufacturing process of LSIs and LCDs, a washing agent for semiconductor substrates, and the like.
Heretofore, as techniques for preparing an aqueous quaternary ammonium hydroxide solution, the following methods are known:
(a) A preparation method which comprises electrolyzing a quaternary ammonium halide obtained by reacting a trialkylamine with an alkyl halide, (b) a preparation method which comprises electrolyzing a quaternary ammonium organic carboxylic acid salt obtained by reacting a trialkylamine with an organic carboxylate (Japanese Patent Application Laid-open No. 100690/1985), (c) a preparation method which comprises electrolyzing a quaternary ammonium inorganic acid salt obtained by reacting a trialkylamine with a dialkyl carbonate (Japanese Patent Application Laid-open No. 170588/1986 and U.S. Pat. No. 4,634,509), and the like.
However, in the above-mentioned preparation method (a), halogen ions and a halogen gas which are harmful and corrosive are formed at high concentrations in an anode chamber in an .electrolysis step, so that some troubles take place, and for example, an anode itself and a device such as an electrolytic tank are corroded. In addition, part of the halogen ions present in the anode chamber pass through a cation exchange membrane and transfer to a cathode chamber at the time of the electrolysis, or the product is contaminated with impurities as a result of the above-mentioned corrosion sometimes, so that the purity of the aqueous quaternary ammonium hydroxide solution produced in the cathode chamber tends to deteriorate. For these reasons, the above-mentioned preparation process (a) is not preferable as the method for preparing the high-purity aqueous quaternary ammonium hydroxide solution.
On the other hand, in the above-mentioned method (b), corrosive organic acid ions such as formic acid ions are formed in the electrolysis step, and the anode itself and a device such as an electrolytic tank are liable to be corroded. As measures against the corrosion, it has been tried to electrolytically oxidize the carboxylic acid ions into a harmless carbon dioxide gas, but in this process, a large amount of electrical energy is inconveniently required. In the case of the electrolysis method using the cation exchange membrane, part of the organic acid ions pass through the ion exchange membrane and transfer into a cathode chamber, or the product is contaminated with impurities as a result of the above-mentioned corrosion sometimes, and also in this case, the purity of the aqueous quaternary ammonium hydroxide solution produced in the cathode chamber tends to deteriorate. In consequence, the above-mentioned preparation process (b) is not preferable as the method for preparing the high-purity aqueous quaternary ammonium hydroxide solution.
In addition, the above-mentioned preparation method (c) is a technique which comprises electrolyzing a quaternary ammonium inorganic acid salt obtained by using, as a raw material, a dialkyl carbonate prepared from phosgene and an alcohol. However, a chlorine compound derived from phosgene tends to be mixed with the above-mentioned raw material dialkyl carbonate, so that the aqueous quaternary ammonium hydroxide solution was contaminated, which often disturbs the manufacture of the desired high-purity aqueous quaternary ammonium hydroxide solution. In addition, the manufacturing cost of the dialkyl carbonate as the raw material is high in the case of a present technique, and therefore this method is not always suitable to prepare the inexpensive aqueous quaternary ammonium hydroxide solution.
As understood from the foregoing, the already known various methods for preparing the high-purity aqueous quaternary ammonium hydroxide solution have many problems, and thus it has been desired to develop a method for preparing the high-purity aqueous quaternary ammonium hydroxide solution at a low cost.